May 2017

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May 2017

Precipitation, relative humidity and soil moisture for May 2017

The surface hydrological variables are more difficult to observe and analyse than surface temperature. The surface hydrological variables page explains more about the reliability of the data and information presented here, including comparisons with alternative datasets. The data on soil moisture is currently of qualitative rather than quantitative value. This summary is intended to provide European and near-global views of conditions for the month. Specific information for many countries can be found on the websites of their weather or climate services.

Anomalies in precipitation, the relative humidity of surface air, the volumetric moisture content of the top 7 cm of soil and surface air temperature for May 2017 with respect to May averages for the period 1981-2010. The darker grey shading denotes where soil moisture is not shown due to ice cover or climatologically low precipitation. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service) Download the original image

May 2017 was in general drier than the 1981-2010 average over much of Europe, in terms of precipitation, surface atmospheric relative humidity and the moisture content of the soil. Conditions were particularly dry (and warm) in the southwest, apart from above-average rainfall over north-western Spain. It was also dry over the Baltic States, Belarus, Ukraine and western Russia, though here temperature was a little below average. Rainfall was higher than average over the southeast of the continent and Anatolia, where relative humidity was around average and soil moisture was mostly below average.

Anomalies in precipitation, the relative humidity of surface air, the volumetric moisture content of the top 7 cm of soil and surface air temperature for June 2016 to May 2017 with respect to 1981-2010. The darker grey shading denotes where soil moisture is not shown due to ice cover or climatologically low precipitation. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service) Download the original image

Precipitation over Europe for the last twelve months has been most below average over northern Spain and France, both in absolute amount (as shown in the above map) and in terms of percentage of normal. Relative humidity and soil moisture were also relatively low in this region, and temperature was relatively high. Precipitation was a little below average over the United Kingdom and much of Scandinavia, though here relative humidity was slightly above average and soil moisture was close to normal. Conditions were dry over the east of the continent and the Middle East. More rain than usual fell over the central Mediterranean.

Anomaly in precipitation, the relative humidity of surface air and the volumetric moisture content of the top 7 cm of soil for May 2017 with respect to May averages for the period 1981-2010. The darker grey shading denotes where soil moisture is not shown due to ice cover or climatologically low precipitation. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service) Download the original image

Rainfall and relative humidity in May 2017 were notably above average over Eritrea, Saudi Arabia and Yemen, where the need to monitor the breeding of desert locusts and, in the case of Yemen, impact on the resurgence of cholera have been reported. Rainfall was much above average in the southern and eastern USA. It was wetter than average over Tibet, but much drier than average over eastern China, in terms of both precipitation and relative humidity.

Southern parts of South America were generally wetter than usual. Relative humidity was well below average over much of Australia and South Africa.

Anomalies in precipitation, the relative humidity of surface air and the volumetric moisture content of the top 7 cm of soil for June 2016 to May 2017 with respect to 1981-2010. The darker grey shading denotes where soil moisture is not shown due to ice cover or climatologically low precipitation. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service) Download the original image

Averages for the past twelve months show particularly dry conditions over the south-eastern USA and eastern Brazil, for all three variables. South Africa also shows up as particularly dry in terms of relative humidity. During May 2017, the country’s Western Cape declared a drought disaster for the province. Relative humidity was also low over much of the Middle East and north-eastern Africa, although the south of Saudi Arabia had above-average rainfall and correspondingly above-average relative humidity over the past twelve months. Much of Canada and Australia were wetter than average.

Monthly anomalies with respect to 1981-2010 in the relative humidity of surface air averaged over all and European land areas, from January 1979 to May 2017. The darker coloured bars denote the May values. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service)Access to data Download the original image

Relative humidity averaged over all land areas declined quite sharply from the late 1990s to the mid 2000s. It had fluctuated around a quite uniform level prior to that, and has fluctuated around a lower level over the past eleven or so years. Values averaged over Europe are more variable, but also show a net decline over time. Corresponding time series of surface humidity show a similar drying.

This drying is not accompanied by an appreciable reduction in precipitation, as shown below for Europe. It may be a consequence of a period in which surface air temperature rose faster over land than it did over sea. Continued monitoring is required to document behaviour over a longer period and refine understanding this aspect of climate variability or change.

The variation over time of the hydrological variables and temperature are shown below for averages over NW, NE, SW and SE Europe. Values are also averaged over successive four-month periods, to enable variations on upwards of the seasonal time scale to be seen more clearly seen than if monthly values had been plotted.

Regional differences are quite pronounced in the time series. Average precipitation rates are higher in the north, particularly the NW, but precipitation is more variable in the southern regions. The latter can also be inferred from maps of the variance of monthly precipitation, so is not simply a consequence of the smaller areas of the southern regions or the four-month averaging. Warming is largest in the NE, but the decrease in relative humidity is larger in the south. The correlations between precipitation, relative humidity and soil moisture evident in the maps of anomalies can be seen to hold on the shorter time scales shown in the time series, but precipitation does not show the marked decrease over time seen for relative humidity and soil moisture.

Running four-month averages of anomalies over NW Europe with respect to 1981-2010 for precipitation, the relative humidity of surface air, the volumetric moisture content of the top 7 cm of soil and surface air temperature, based on monthly values from January 1979 to May 2017. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service)Access to data Download the original image

Running four-month averages of anomalies over NE Europe with respect to 1981-2010 for precipitation, the relative humidity of surface air, the volumetric moisture content of the top 7 cm of soil and surface air temperature, based on monthly values from January 1979 to May 2017. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service)Access to data Download the original image

Running four-month averages of anomalies over SW Europe with respect to 1981-2010 for precipitation, the relative humidity of surface air, the volumetric moisture content of the top 7 cm of soil and surface air temperature, based on monthly values from January 1979 to May 2017. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service)Access to data Download the original image

Running four-month averages of anomalies over SE Europe with respect to 1981-2010 for precipitation, the relative humidity of surface air, the volumetric moisture content of the top 7 cm of soil and surface air temperature, based on monthly values from January 1979 to May 2017. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service)Access to data Download the original image